You’re always hearing that your CD4 count measures how well your immunesystem is doing with HIV. But there’s another measurement to consider:the CD4 “percentage.” This number tells you what percentage of yourlymphocytes (infection- and cancer-fighting white blood cells) is madeup of CD4s. The percentage tends to be more stable than the CD4count—which can drop during short-term events like a yeast infection, avaccine or serious stress. As long as the percentage is safe, temporarydips in count shouldn’t cause alarm. Here’s how four HIV docs surveyedby POZ use CD4 percentages in decision-making:

STARTING MEDS:All say CD4 percentage, CD4 count and viral load should be considered.Many docs suggest starting meds—if a patient is ready to handlethem—after repeated CD4 counts below 300 to 350. As for percentage, arecent study suggests that people with HIV are at risk for illness ifit dips below 17%. “If this appears on two or three reports, I stronglyrecommend starting meds” regardless of CD4 count, says New York City’sLloyd Bailey, MD. Antonio Urbina, MD, also a New Yorker, and Chicago’sBeverly Sha, MD, start at 14%. Lisa Sterman, MD, of San Francisco,doesn’t look for a set CD4 count or percentage, because she finds thateach patient has a variety of numbers and health characteristics toconsider. “And for women, who tend to have lower CD4 counts,” Stermansays, “percentages are more important.”

SWITCHING COMBOS: ForSha and Sterman, changes in viral load, not CD4s, suggest regimenchanges. Urbina adds, “If CD4 count and percentage drop, I look for ahidden infection like TB or syphilis [to explain the drop], rather thanswitching.”  

STARTING PREVENTIVE MEDS: As the immunesystem deteriorates, people with HIV become vulnerable to opportunisticinfections like pneumocystis carinii pneumonia (PCP). Prophylactic(preventive) treatments are available. Federal guidelines (and mostAIDS docs) call for starting PCP prophylaxis at CD4 counts below 200 orCD4 percentages below 14. Preventive treatments for other infectionsare recommended only at lower CD4 counts.